American Petroleum Institute

Evaporation Loss from Internal Floating-Roof Tanks - THIRD EDITION
 N PUBL 2519

Annotation

This publication contains an improved method for estimating total evaporative losses and/or the equivalent atmospheric hydrocarbon emissions from freely vented internal floating-roof tanks containing multi-component hydrocarbon mixtures (such as crude oils and gasolines), as well as single component stocks (such as petrochemicals). It was developed by the Committee on Evaporation Loss Measurement of the American Petroleum Institute. The equations presented are based on recent laboratory, test tank, and field tank data. These equations are intended to provide loss estimates for general equipment types, since it is not within the scope of this publication to address specific proprietary commercial equipment designs.

Internal floating-roof tanks addressed in this publication include: (1) tanks with fixed roofs supported by columns within the tank (column-supported), which are typical of fixed-roof tanks fitted with an internal floating deck; and (2) tanks with fixed roofs that do not require column support (self-supporting), which are typical of external floating-roof tanks covered with a fixed roof. Tanks initially constructed with both a fixed roof and a floating deck may be of either type. Typical currently available floating decks, deck fitting details, and rim seal systems are described for information only. This publication is not intended to be used as a guideline for equipment design, selection, or operation.

The equations are intended to be used to estimate annual losses from internal floating-roof tanks, for various general types of tanks, floating decks, and rim seal systems, as well as for various liquid stocks, stock vapor pressures, and tank sizes. The equations are applicable to properly maintained equipment in normal working conditions. The equations have been developed for liquids that are not boiling, with a true vapor pressure ranging from approximately 0.1 to less than 14.7 pounds per square inch absolute. Without detailed field information, the estimating techniques become more approximate when used to calculate losses for time periods shorter than 1 year.